The invention generally relates to electronics circuits. The invention more particularly relates to dynamic matching in cascode circuits, for example, cascode circuits that are used to provide adjustable gain of an input signal.
In analog electronic circuits, amplifiers are constructed in many configurations and have various parametric tradeoffs. Discrete dual gate MOSFET (metal-oxide semiconductor field-effect transistor) based amplifiers have been used as IF (intermediate frequency) amplifiers with adjustable gain. In such amplifiers the two gates of the dual gate MOSFET may be arranged as a common source device (transistor) feeding a common gate devicexe2x80x94i.e., as a cascode. The common source transistor receives the input signal and the combination of the common gate and common source transistors control the gain and provide isolation. Such amplifiers have good dynamic range, noise figure and reverse isolation. However, they may suffer from distortion at low gain settings and their input impedance may vary with gain.
There is a need to provide amplifiers having controllable gain, good dynamic range, noise figure and reverse isolation but also suitable for higher operating frequencies (microwave rather than IF) and having excellent input match at both high and low gain settings.
Accordingly, the invention provides amplifiers with superior performance and input matching. Such an amplifier may be implemented as an IC (integrated circuit) with CMOS (complementary metal-oxide semiconductor) or other semiconductor technologies such as GaAs (Gallium Arsenide). High operating frequency (e.g., microwave) may be supported through LSI (large scale integration), as is well-known in the art. Superior performance results from aspects of the novel designs.
According to a first aspect of the invention, a method for improving an input match in a circuit is presented. The method may comprise: operating a cascode having a stage gain controlled by a level setting gain control voltage and operating an impedance compensating circuit. The impedance compensating circuit may controlled by the same level setting gain control voltage.
According to a further aspect of the invention, a circuit for processing a signal comprising is presented. The circuit may include a cascode, a gain controller controlling a gain of the cascode; and an impedance controller loading an input impedance of the cascode with a loading impedance responsive to the control signal. The circuit may operate with adjustable gain and compensated impedance.